Remove newline from default public_net_name

The public network name is set via public_net_name, and its default
value is the first item in the external_net_names list. The variable
uses the YAML folded block scalar notation, but does not use the
chomping indictator, which means the string is assigned a trailing
newline.

This change fixes the issue by adding the chomping indicator.

Change-Id: I68fb65cd3bc7c4390813747f9ac4ecebc3b4145f
Story: 2007654
Task: 39731

ansible/group_vars/all/network

@@ -35,7 +35,7 @@ external_net_names: >
      ['external_net'] }}
 
 # Name of the network used to expose the public OpenStack API endpoints.
-public_net_name: >
+public_net_name: >-
   {{ external_net_names[0]
      if external_net_names | length > 0 else
      None }}

releasenotes/notes/fix-default-public-net-name-067338275460b50d.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixes an issue where the default value of ``public_net_name`` included a
+    trailing newline. See `story 2007654
+    <https://storyboard.openstack.org/#!/story/2007654>`__.
+